The 23-year-old Downton Abbey star is believed to be the favourite to land the role in forthcoming movie Captain America: The Winter Soldier - the sequel to last year's Marvel action movie Captain America.
They are all said to be auditioning for the role, which would see them star opposite Chris Evans, who is to reprise his role as Steve Rogers/Captain America in the forthcoming film.
Frank Grillo is in line to play villain Crossbones in the Marvel movie and Sebastian Stan has been linked to the role of The Winter Soldier.
Captain America: The Winter Soldier is set to be released in April 2014, and will also see Anthony Mackie portray Falcon and Scarlett Johansson reprise her role as Natasha Romanoff/Black Widow.
Brunette beauty Hayley Atwell starred as Captain America's love interest in the original motion picture last year, and she recently joked it was enjoyable to have a "bit of a grope" of Evans' chest during filming.
She said: "When I touched his man chest it was literally just an impulse for me that I had and I needed to touch it to make sure it was real. I had to have a bit of a grope for all the other ladies watching, I felt like it was my duty."
